The invention relates to a device for controlling a transport of printing products by a print-related machine.
For controlling and regulating sheet-feeding into a printing machine, and advancing or conveying sheets through a printing machine, it has become known heretofore to provide stationary photoelectric detectors in the conveyance path of the sheets, which operate by reflection or by transmitted light. In this regard, both sheet edges as well as markers that were specifically applied for the control or regulation can be detected. Furthermore, photoelectric detectors have become known heretofore which detect the entire surface of a printing product, adjustment values for adjustment elements being differentiated from received image signals, and serving to control the position of a printing image on the printing product, the position of colors that are to be printed overlappingly onto the printing product, and the thickness of the layers of colors that have to be printed overlappingly (note the published German Patent Document DE 43 21 179 A1).
Heretoforeknown devices of this general type have the disadvantage that they are not applicable for a wide variety of printed-material types. The application of additional markers limits the printable area that is available. Those devices, which are constructed for several types of printed material, usually include detectors based on different physical principals. Such detectors require considerable material and are costly.
In U.S. Pat. No. 5,689,757, a device for measuring the roughness of printed materials is described. The roughness is determined by two detectors which detect the intensity of reflected and dispersed measuring light. The measurement value for the roughness serves for setting parameters of an electrographic machine.
For examining the surface characteristics of materials, it has become known heretofore to examine the surfaces with coherent laser light.
The topography and the micro-roughness distribution, respectively, located on the surface at the location of the measuring light causes stray light, which can be recorded with a camera. An incident measuring-lightwave train is modified with reflections on a surface in phase and amplitude. Due to a superimposition of reflecting wave trains, a stray-light distribution is created, which is characteristic for the surface topography. This phenomenon is described as speckles effect. For each element of the surface, a characteristic black-and-white pattern, a so-called speckle pattern, is created. Speckle images can be analyzed or evaluated with the aid of digital image processing through mathematical correlation procedures. By joining the speckle pattern with the characteristic micro-roughness distribution of the viewed surface element, a shifting of the surface in the space leads to an adequate shifting of the speckle pattern in the space. On the Internet, according to http://online.tu-graz.ac.at/tug online g/forschung/FA F159 2324 g.html on Sep. 8, 1999, a device for measuring the expansion or extension of the material has been described, with which the context of the shifting of a correlation-maximum was examined together with the real or actual shifting of a sample.
In the published German Patent Document DE 195 09 962 A1, a method is described for determining all three spatial components of a shifting-vector field of an object-surface, wherein a method for pattern matching for determining two components of the shifting-vector field is combined with a method for comparing contours of the object for determining the third component.
On the Internet on Sep. 8, 1999 according to http://www.msr.uni-bremen.de/andreas/cio 998. htm, a device for measuring the surface-roughness was described, wherein a CCD-camera was used to record a polychromatic stray-light speckle pattern, which allows a short-term recording with an exposure time of {fraction (1/500,000)} second or less.
The foregoing stray-light measuring devices were either laid-open for measurements with samples at rest or for measurement with moving samples, the movement of the sample during the image recording being considered to be unwanted and being calculated out accordingly.
It is accordingly an object of the invention to provide a device for controlling a transport of printing products through a print-related machine, which is able to be used for a wide variety of materials and which allows a determination of the position of the printing product or of individual surface-elements of the printing product during movement thereof.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for controlling the transport of a printing product by a print-related machine, comprising at least one locally stationary photoelectric detector having a light transmitter, by which light is directed at a surface of the printing product, and at least one light receiver for detecting the light remitted from the surface, and a device for evaluating the remitted light, the evaluating device having computational equipment connected to adjustment elements for controlling the effect of a cyclically operating transport device, the light transmitter including a light source for transmitting coherent light, the light receiver including an element for recording a spatial distribution of stray light, and a timing device provided for synchronizing the instant of time of the recording with the cycle of the transporting device, the evaluation device having a comparator for local distribution of the stray light with a prescribed distribution at the instant of time of the recording.
In accordance with a concomitant feature of the invention, the recording element is one of an optical CCD-area and CCD-line and an arrangement of single photo-diodes, respectively.
Due to the lighting with laser light of an area of a printing product, there is created, as a result of the roughness of the printing product, a characteristic gray-value distribution in the form of a pattern with light and dark speckle-points. The size of the speckles depends upon the roughness of the surface and upon the aperture of the optic system of the light-receivers. By modifying the aperture and the diameter, respectively, of an aperture diaphragm, via the spectrum of all printed materials and all printed-material roughnesses, respectively, an optimal point-extension or expansion of the speckles can be set for the light receiver. By a reduction in the width of the diaphragm aperture of a receiver-lens, speckles which are very large can also be created with smooth printed-material surfaces, as would otherwise only be formed for roughened surfaces. A defined roughness is present at a predetermined location on the printing product, which results in a characteristic speckle-image. The characteristic speckle-image can only be seen in the light-receiver, but not on the printing product. A shifting of the lit-up area of the printing product results in a shifting of the speckles in the space. This shifting-vector can be determined in different ways, for example, with methods for pattern-recognition. If a line-shaped light-receiver is used, then, with a shifting of the printing product, a given or determined speckle is located at a different position of the sensor-line. The invention can serve for determining the register of a printing-image on the printing product and for position-recognition of the printing product. If the device is directed onto a printed material web, one can then deduce the speed and the acceleration of the web from the timely diversions of the speckle shifts. Applications for monitoring the web flow and for web-tear control result therefrom. From spatial diversions of the shifting, values for the web-extension or web-tension are obtained.
The invention is applicable for printing machines for processing or conveying sheets or webs.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for controlling a transport of printing products through a print-related machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, where in: